The present invention relates to a portable communication terminal and, more particularly, to a portable communication terminal having a light emission unit for operation buttons which use light-emitting diodes.
In general, a portable communication terminal represented by a portable telephone has built-in light-emitting diodes (to be referred to as “LEDs” hereinafter) to illuminate operation buttons so that the buttons can be operated even in the darkness.
Light emission of the LEDs of an electronic device in a general portable communication terminal will be described with reference to FIGS. 6A to 6C and FIG. 7.
FIGS. 6A to 6C and FIG. 7 schematically show a conventional electronic device. An electronic device 101 includes a front case 102 and rear case 103.
The front case 102 is a case that forms the surface front side of the electronic device 101, and the rear case 103 is a case that forms the rear surface side of the electronic device 101. The front case 102 has an operating portion 104 and display 105.
The front case 102 has a plurality of openings 102c to place operation buttons 106. The portions between the openings 102c are narrow, and the front case 102 is thin, leading to a low rigidity.
The operation buttons 106 are the components for operating the electronic device 101, and are arranged such that their heads project from the corresponding openings 102c. 
A rubber sheet 107 is adhered to the lower surfaces of the operation buttons 106 in the electronic device 101. When an operation button 106 is pressed, the corresponding portion of the rubber sheet 107 is also pressed together with the operation button 106. Those portions of the rubber sheet 107 which are immediately under the operation buttons 106 have downward projections 107a. The projections 107a abut against metal dome contacts 109 through a light-diffusing sheet 108. The side edges of the rubber sheet 107 are sandwiched by the front case 102 and a substrate 111.
LEDs 110 are placed between metal domes on the substrate 111.
In general, when the power supply of a portable communication terminal is turned on, the LEDs of the light emission structure described above emit light. For example, in the case of a folding portable telephone, when the portable telephone is opened, the power supply is turned on and the LEDs emit light.
Light from the LEDs 110 is transmitted through the rubber sheet 107 directly or after being reflected by the light-diffusing sheet 108 to propagate to the operation buttons 106. Thus, the respective operation buttons 106 are illuminated.
In a portable terminal represented by such a portable telephone, the weight of the casing portion has been decreased and the internal structure has been improved largely to achieve downsizing and weight reduction (for example, Japanese Patent Laid-Open No. 11-213793 (FIG. 1), Japanese Patent Laid-Open No. 6-275169 (FIG. 1), and Japanese Utility Model Laid-Open No. 5-031039 (FIG. 1).
Hence, the portable communication terminal has achieved downsizing and weight reduction.
As the portable communication terminal is downsized and reduced in weight, however, the operation buttons 106 also become small and are arranged close to each other on the front surface side of the front case. Accordingly, sometimes the operator may erroneously press a casing portion 102a in the vicinity of an operation button.
At this time, as the casing portion 102a in the vicinity of the pressed operation button has a low rigidity, when the casing portion 102a is pressed, it is bent and the corresponding operation button 106 is also pressed. As a result, the portable communication terminal may operate erroneously.
From the viewpoint of weight reduction and power consumption reduction of the portable communication terminal, to decrease the number of LEDs of the light emission structure used in the electronic device is sought for. When, however, the number of LEDs used in the electronic device is decreased, although the operation buttons 106 placed near the LEDs 110 are illuminated brightly, the operation buttons 106 placed far from the LEDs 110 are illuminated only dimly. Thus, a difference in emitted light brightness occurs among the operation buttons to cause so-called light nonuniformity.